The present invention relates to imaging systems and, more particularly, to imaging systems in which perceived depth-of-field can be enhanced by digital image processing.
Electronic devices such as cellular telephones are often provided with camera sensors. Users of these devices are increasingly demanding the ability to capture high quality images. One factor in determining image quality is depth of field. The depth of field in an image is the range of distances over which the image appears to be in focus. In an image with a shallow depth of field, only objects that are close to the plane of focus will appear sharp and in focus. Objects in an image with a shallow depth of field image that lie in front of the plane of focus or behind the plane of focus will be blurred. Images with a large depth of field appear sharp over a greater distance. In this type of scenario, even objects that lie significantly off the plane of focus will appear to be sharp.
One way to obtain an image with a large depth of field involves reducing the aperture of the camera lens. This process, which is sometimes referred to as “stopping down” the lens can only be used in devices with adjustable-aperture lenses. The use of a small aperture to enhance depth of field may also require the use of a long exposure time, which can lead to reductions in image quality due to camera shake or subject motion.
Another way in which to obtain images with enhanced depth of field involves the use of so-called extended depth of field (EDoF) lenses. EDoF systems are optimized to improve depth of field at the expense of peak image sharpness. Digital image processing techniques may be used to sharpen and smooth images captured with EDoF systems to improve perceived quality and thereby compensate for the reduction in sharpness that is imposed by the EDoF lens. Although such systems may be satisfactory in certain circumstances, the use of EDoF lenses poses challenges. For example, the manufacturing techniques used to produce EDoF lenses tend to increase the cost and complexity of imaging systems in which EDoF lenses are used.
Specialized cameras called “array cameras” that can manipulate depth of field through digital processing are available, but these cameras must process data from a grid made up of numerous independent image sensors. Array cameras can therefore be even more complex, costly, and bulky than cameras with EDoF lenses.